Conventionally, a parking brake is used for restricting movement of a parked vehicle. For example, a manual parking brake is used in which an operation force applied to an operation lever is transmitted to a brake mechanism of the parking brake when the operation lever pulls a brake cable caused by the operation force. An electrically driven parking brake is also used in which a rotational force of a motor is transmitted to the brake mechanism of the parking brake.
In the electrically driven parking brake (i.e. EPB), a brake force is generated when, for example, a rotational force of a motor pulls a brake cable and the tension of the brake cable is thereby transmitted to the brake mechanism (i.e. actuator). In a lock control of the EPB, the parking brake control device rotates the motor in a lock side direction (i.e. forward direction) to transmit the rotational force of the motor to the brake mechanism (i.e. actuator) and stops the rotation of the motor with the brake force remained. In a release control, the parking brake control device rotates the motor in a release side direction (i.e. reverse direction) to remove the brake force.
Thus, the lock/release control includes the lock control and the release control. In the lock control, the parking brake control device keeps the EPB locked at a desired force by stopping the rotation of the motor in the lock side direction when the tension applied to the brake cable reaches a target value. In the release control, the parking brake control device detects that the brake force is removed by detecting that the tension of the brake cable becomes approximately zero. See Japanese Patent Application Publication No. 2001-514597 (U.S. Pat. No. 6,249,737).